The present invention is directed to a process for preparing photopatternable polymers and to thermal ink jet print heads generated with the photopatternable polymers. More specifically, the present invention is directed to a process for the functionalization, for example, acrylation, methacrylation, or aminoalkylacrylation, of polymers containing halogenated aromatic mers or monomers, for example, homopolymers of poly(haloalkylstyrene) and random copolymers comprised of polystyrene and poly(haloalkylstyrene), and subsequent patterning. In embodiments of the present invention, there are provided processes for the preparation of an intermediate molecular weight, narrowly dispersed, poly(haloalkylstyrene) or copoly(haloalkylstyrene-styrene) using a stable free radical moderated polymerization procedure, followed by reacting these polymers with a reactive acrylate, alkacrylate salt, or an alkylaminoacrylate in, for example, sequential reactions, or alternatively, by a one pot procedure thereby forming a photopatternable acrylated, alkacrylated, or alkylaminoacrylated polymer. The acrylated, alkacrylated, or alkylaminoacrylated polymer can be conveniently and readily cross-linked when exposed to radiation of, for example, less than about or equal to about 400 nanometers.
In microelectronics applications, there is a great need for low dielectric constant, high glass transition temperature or highly crosslinked, thermally stable, photopatternable polymers for use as interlayer dielectric layers and as passivation layers which protect microelectronic circuitry. Poly(imides) are widely used in attempts to satisfy these needs; these materials, however, have disadvantageous characteristics such as relatively high water sorption and hydrolytic instability. Thus, there is a need for high performance polymers which can be effectively photopatterned and developed at high resolution.
One particular application for such materials is the formulation of ink jet print heads. Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, these systems are much simpler than the continuous stream type. There are different types of drop-on-demand ink jet systems. One type of drop-on-demand system has as major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality images. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
Another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing s digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which heat is dissipated by vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The surface of the printhead encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after about 100 to about 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened.